Short-Circuit Resistance Capacity of a 250MVA High-Power Transformer DRAGOS PASCULESCU 1 , ANDREI ROMANESCU 2 , VLAD-MIHAI PASCULESCU 3 REMUS DOBRA , University of Petrosani 4 1, 4 , Transelectrica Romanian Power Grid Company 2 , INCD INSEMEX 3 20 Universității Street, Postcode: 332006, Petroșani, Hunedoara County 3 Corneliu Coposu Boulevard, Postcode: 550253, Sibiu, Sibiu County 1, 4 32-34 G-ral Vasile Milea Street, Postcode: 332047, Petroșani, Hunedoara County 2 3 ROMANIA pdragos_74@yahoo.com 1 , romanescu.andrei@transelectrica.ro 2 , vlad.pasculescu@insemex.ro 3 , dobraremus@yahoo.com 4 Abstract: - This paperwork mainly aims to describe the tests that are being carried out in specialized laboratories for high-power transformers testing. The purpose of testing transformers used in the transmission and distribution of electricity is to have an imprint of the data which characterize the technical status resulted from the manufacturing of the high-power transformer as well as to observe its behavior in operation. Key-Words: high-voltage laboratory, high-power transformer, parameters, short-circuit, technical status, testing 1 Introduction The large companies manufacturing transformers usually dispose of testing laboratories for the manufactured transformers. This paper focuses on the presentation of the test method for detecting the short-circuit resistance capacity of the 250 MVA transformer in the Končar – Siemens laboratory from Croatia. In the testing laboratory, the transformer has been subjected to other prophylactic tests, most of them being carried out during the annual inspections, as following: - Summary dielectric test and oil test; - Measurement of voltage ratio and check of connection symbol; - Measurement of winding resistance; - Impedance and load loss measurement; - Measurement of no-load loss and current; - Induced overvoltage withstand test and partial discharge measurement; - Separate source voltage test; - Operation test on on-load tap-changer; - Measurement of the zero-sequence impedance; - Capacitance and the insulation power factor measurement; - Insulation resistance measurement; - Temperature rise test and tightness (leakage) test; - Lightning impulse test, test with chopped on the tail and switching impulse test; - Measurement of acoustic sound level; - Measurement of higher harmonics in magnetizing current. 2 Main Technical Characteristics of the High-Power Transformer The tested transformer will be used in Brasov 400/110kV Power Station, which is a major junction of CNTEE Transelectrica SA – Romanian Power Grid for circulating the power transit, ensuring in this way the electricity supply of Brasov County, also being ensured the stability in electricity supply of the 110kV inter-county networks. [4] - Nominal voltage: 250000 / 250000 / 80000 kVA with OFAF cooling - Applicable standards: IEC - Nominal voltage ratio: 400 000 V ±8 x 1.56% / 121 000 V / 20 000 V - Voltages and currents (Table 1): Recent Advances in Electrical Engineering ISBN: 978-960-474-318-6 167